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- var isObject = require('./isObject'),
- now = require('./now'),
- toNumber = require('./toNumber');
-
- /** Error message constants. */
- var FUNC_ERROR_TEXT = 'Expected a function';
-
- /* Built-in method references for those with the same name as other `lodash` methods. */
- var nativeMax = Math.max,
- nativeMin = Math.min;
-
- /**
- * Creates a debounced function that delays invoking `func` until after `wait`
- * milliseconds have elapsed since the last time the debounced function was
- * invoked. The debounced function comes with a `cancel` method to cancel
- * delayed `func` invocations and a `flush` method to immediately invoke them.
- * Provide `options` to indicate whether `func` should be invoked on the
- * leading and/or trailing edge of the `wait` timeout. The `func` is invoked
- * with the last arguments provided to the debounced function. Subsequent
- * calls to the debounced function return the result of the last `func`
- * invocation.
- *
- * **Note:** If `leading` and `trailing` options are `true`, `func` is
- * invoked on the trailing edge of the timeout only if the debounced function
- * is invoked more than once during the `wait` timeout.
- *
- * If `wait` is `0` and `leading` is `false`, `func` invocation is deferred
- * until to the next tick, similar to `setTimeout` with a timeout of `0`.
- *
- * See [David Corbacho's article](https://css-tricks.com/debouncing-throttling-explained-examples/)
- * for details over the differences between `_.debounce` and `_.throttle`.
- *
- * @static
- * @memberOf _
- * @since 0.1.0
- * @category Function
- * @param {Function} func The function to debounce.
- * @param {number} [wait=0] The number of milliseconds to delay.
- * @param {Object} [options={}] The options object.
- * @param {boolean} [options.leading=false]
- * Specify invoking on the leading edge of the timeout.
- * @param {number} [options.maxWait]
- * The maximum time `func` is allowed to be delayed before it's invoked.
- * @param {boolean} [options.trailing=true]
- * Specify invoking on the trailing edge of the timeout.
- * @returns {Function} Returns the new debounced function.
- * @example
- *
- * // Avoid costly calculations while the window size is in flux.
- * jQuery(window).on('resize', _.debounce(calculateLayout, 150));
- *
- * // Invoke `sendMail` when clicked, debouncing subsequent calls.
- * jQuery(element).on('click', _.debounce(sendMail, 300, {
- * 'leading': true,
- * 'trailing': false
- * }));
- *
- * // Ensure `batchLog` is invoked once after 1 second of debounced calls.
- * var debounced = _.debounce(batchLog, 250, { 'maxWait': 1000 });
- * var source = new EventSource('/stream');
- * jQuery(source).on('message', debounced);
- *
- * // Cancel the trailing debounced invocation.
- * jQuery(window).on('popstate', debounced.cancel);
- */
- function debounce(func, wait, options) {
- var lastArgs,
- lastThis,
- maxWait,
- result,
- timerId,
- lastCallTime,
- lastInvokeTime = 0,
- leading = false,
- maxing = false,
- trailing = true;
-
- if (typeof func != 'function') {
- throw new TypeError(FUNC_ERROR_TEXT);
- }
- wait = toNumber(wait) || 0;
- if (isObject(options)) {
- leading = !!options.leading;
- maxing = 'maxWait' in options;
- maxWait = maxing ? nativeMax(toNumber(options.maxWait) || 0, wait) : maxWait;
- trailing = 'trailing' in options ? !!options.trailing : trailing;
- }
-
- function invokeFunc(time) {
- var args = lastArgs,
- thisArg = lastThis;
-
- lastArgs = lastThis = undefined;
- lastInvokeTime = time;
- result = func.apply(thisArg, args);
- return result;
- }
-
- function leadingEdge(time) {
- // Reset any `maxWait` timer.
- lastInvokeTime = time;
- // Start the timer for the trailing edge.
- timerId = setTimeout(timerExpired, wait);
- // Invoke the leading edge.
- return leading ? invokeFunc(time) : result;
- }
-
- function remainingWait(time) {
- var timeSinceLastCall = time - lastCallTime,
- timeSinceLastInvoke = time - lastInvokeTime,
- timeWaiting = wait - timeSinceLastCall;
-
- return maxing
- ? nativeMin(timeWaiting, maxWait - timeSinceLastInvoke)
- : timeWaiting;
- }
-
- function shouldInvoke(time) {
- var timeSinceLastCall = time - lastCallTime,
- timeSinceLastInvoke = time - lastInvokeTime;
-
- // Either this is the first call, activity has stopped and we're at the
- // trailing edge, the system time has gone backwards and we're treating
- // it as the trailing edge, or we've hit the `maxWait` limit.
- return (lastCallTime === undefined || (timeSinceLastCall >= wait) ||
- (timeSinceLastCall < 0) || (maxing && timeSinceLastInvoke >= maxWait));
- }
-
- function timerExpired() {
- var time = now();
- if (shouldInvoke(time)) {
- return trailingEdge(time);
- }
- // Restart the timer.
- timerId = setTimeout(timerExpired, remainingWait(time));
- }
-
- function trailingEdge(time) {
- timerId = undefined;
-
- // Only invoke if we have `lastArgs` which means `func` has been
- // debounced at least once.
- if (trailing && lastArgs) {
- return invokeFunc(time);
- }
- lastArgs = lastThis = undefined;
- return result;
- }
-
- function cancel() {
- if (timerId !== undefined) {
- clearTimeout(timerId);
- }
- lastInvokeTime = 0;
- lastArgs = lastCallTime = lastThis = timerId = undefined;
- }
-
- function flush() {
- return timerId === undefined ? result : trailingEdge(now());
- }
-
- function debounced() {
- var time = now(),
- isInvoking = shouldInvoke(time);
-
- lastArgs = arguments;
- lastThis = this;
- lastCallTime = time;
-
- if (isInvoking) {
- if (timerId === undefined) {
- return leadingEdge(lastCallTime);
- }
- if (maxing) {
- // Handle invocations in a tight loop.
- timerId = setTimeout(timerExpired, wait);
- return invokeFunc(lastCallTime);
- }
- }
- if (timerId === undefined) {
- timerId = setTimeout(timerExpired, wait);
- }
- return result;
- }
- debounced.cancel = cancel;
- debounced.flush = flush;
- return debounced;
- }
-
- module.exports = debounce;
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